In drilling operations, wellbores are generated in subsurface rock formations for purposes that include the extraction of resources from subterranean reservoirs. Drilling techniques may be varied in some settings to create deviated wellbores to place the wellbore within a particular region, or between stratigraphic layers and other features present within the formation. In directional drilling, for example, a wellbore may exhibit a vertical trajectory initially and, at a later depth, wellbore trajectory may be deviated using one or more types of directional drilling tools and procedures.
Deviated and horizontal wells produced from directional drilling may be useful in some applications to enhance the development of unconventional reservoirs, particularly when combined with enhanced oil recovery techniques such as hydraulic fracturing. However, structural interpretation of deviated and horizontal wells may be challenging in heterogeneous formations containing varying stratigraphic composition, layering, and bed orientation, because a wellbore may pass through the same stratigraphic layer multiple times, creating difficulty in aligning and correlating measurement signatures in data acquired from the formation.
Proper characterization of the formation using data generated from various downhole tools is an important factor in guiding well placement into a given zone of interest. The selected wellbore path for directional drilling may be predetermined in some cases based on interpretation of the 3D geometry of the stratigraphic layering of the subsurface formations, prior to initiation of drilling operations. In other drilling methods, such as logging-while-drilling (LWD) and geosteering, formation characterization may occur during the excavation of a wellbore, or shortly thereafter, through the use of tools integrated into a bottomhole assembly or along a drillstring. LWD may have advantages in some scenarios, particularly when there is concern that formation properties will be altered by the invasion of wellbore fluids or where the use of wireline tools may be difficult.